The present disclosure relates to a wireless communication apparatus mounted with plural communication functions conforming to different wireless communication standards, and, more particularly to a wireless communication apparatus mounted with two different communication functions that use an identical frequency band.
More specifically, the invention relates to a wireless communication apparatus mounted with both a wireless LAN function represented by IEEE802.11 and a Bluetooth communication function, and, more particularly to a wireless communication apparatus that simultaneously uses two incompatible communication functions without causing radio interference.
The wireless LAN attracts attention as a system that releases users from LAN wiring in the wired system. As an example of the standard concerning a wireless network, there is IEEE (the Institute of Electrical and Electronics Engineers) 802.11. It is possible to perform wireless data transmission using a global radio frequency called an ISM (Industry Science Medical) band. Recently, a broadband Internet connection service that uses a Wireless LAN represented by “Hot Spot” is widely used. This makes it possible to use the Internet even in service areas provided in facilities outside homes and offices such as cafeterias, hotels, fast food restaurants, stations, and airports. Thus, the wireless LAN function is often mounted in mobile terminals such as cellular phones and PDAs (Personal Digital Assistants).
On the other hand, there is known Bluetooth communication as a standard for providing a wireless connection interface applicable to various industries. The “Bluetooth SIG (Special Interest Group)” is entrusted with operation and management of the Bluetooth communication. The Bluetooth communication is characterized by lower consumption and short distance communication, although the ISM band is used. An overall data transmission rate of the Bluetooth communication is 1 Mbps. As major applications of the Bluetooth communication, sound communication between a telephone body and a handset and transmission of audio data from audio equipment to a headphone are assumed.
Recently, there is an increasing demand for mounting of a Bluetooth communication function in the mobile terminals such as the cellular phones and the PDAs together with the wireless LAN function. With a communication terminal that has a double communication mode of the wireless LAN and the Bluetooth communication, a user can make connection to the Internet through an access point of the wireless LAN and download desired data contents and, moreover, send audio reproduction data to a headset according to the Bluetooth communication and appreciate music.
When the wireless LAN and the Bluetooth communication are mounted in the same terminal, transceiver modules of both the communication systems are basically realized as separate units independent from each other. However, it is possible to share several components such as a filter, an antenna, and an RF switch.
However, these communication standards that use the same frequency band, that is, the ISM band, do not have compatibility. Thus, when the user attempts to perform communication using both the communication standards simultaneously, the communication standards interfere with each other to cause radio interference and reception failure. In other words, when transceivers of the respective communication systems include independent antennas, a signal discharged to the air from the antenna of one transceiver is received by the antenna of the other transceiver to cause radio interference. When one transceiver outputs strong high-frequency power near the other transceiver, it is likely that an RF reception circuit of the other transceiver is permanently damaged. When both the transceivers share an antenna, if, during a period in which one transceiver is performing transmission, the other transceiver performs a reception operation, a return current is generated at a connection point for sharing the antenna to cause radio interference.
Therefore, an operation of the other transceiver has to be stopped while one transceiver is operating. Even if a terminal is mounted with both the communication functions of the wireless LAN and the Bluetooth communication, it is difficult to perform audio reproduction using the Bluetooth communication during data transmission through the wireless LAN. It is also difficult to make an Internet connection through the wireless LAN during a call that uses the Bluetooth communication. Thus, it is difficult to sufficiently enjoy the merits of the functions of the double communication
For example, there is proposed a multi-transceiver mobile terminal that is mounted with both the communication functions of the wireless LAN and the Bluetooth communication and efficiently share a diversity antenna (see, for example, JP-A-2001-24579). The mobile terminal includes two diversity antennas connected in first and second antenna ports, respectively. In a Bluetooth operation mode, the second antenna port is connected to a Bluetooth-transceiver input/output port and a wireless LAN transmission/reception port is disconnected from the second antenna port. In a wireless LAN transmission mode, the wireless LAN transmission/reception port is connected to the first antenna port and the Bluetooth-transceiver input/output port is disconnected from the second antenna port. When the Bluetooth-transceiver input/output port is disconnected from the second antenna port in the wireless LAN reception mode, the wireless LAN transmission/reception port is connected to one of the antenna ports.
In other words, in this mobile terminal, high-frequency switches are combined to contrive a switching algorithm thereof, whereby sharing of the pair of diversity antennas by the respective transceivers of the wireless LAN and the Bluetooth communication is realized. However, since radio interference is prevented by changing over the high-frequency switches, a circuit is complicated and high-frequency switching units are necessary, causing an increase in cost. Further, a control circuit for controlling the high-frequency switching units and software for working the control circuit are also necessary, resulting in an increase in size of an overall system. Moreover, since communication modules connected to the antennas are selected by changing over the switches, during operation of one communication function, the other communication function may have to be stopped.